Keigo KITAKUNI

Exterior Damege Survey for Prediction of Internal Deterioration of Concrete

Fuminori NAKAMURA

In Japan, many of civil engineering structures were constructed during the high economic growth period, and 50 years have passed since then. There is concern that maintenance costs for these bridges will increase rapidly in the future. It is necessary to reduce costs by improving the efficiency of maintenance management. Damage such as cracks, rust, and spalling appears on the surface of concrete structures that have been damaged by salt. Therefore, as a study to improve efficiency, this research used the removed Omi River Bridge to investigate the relationship between the exterior damage and the degree of internal deterioration. The lower flange of the superstructure T-girder was the target of the survey, and the nuclear specimen was divided into three surfaces: sea side, lower side, and mountain side.
First, exterior damage survey were conducted to measure crack widths using a crack scale, linear axial lengths of cracks, and floating and spalling areas using a percussion hammer. As a result, it was confirmed that crack length and width were generally larger at the sea side, and that cracks were larger on the mountain side of the specimen closest to the sea. 
Next, the amount of permeated chloride ions and steel corrosion were measured in the internal degradation survey. As a result, it was confirmed that the chloride ion concentrations were larger at sea level for all specimens. And it was confirmed that shear reinforcement corroded in all specimens and that corrosion of PC steel and axial rebar tended to occur in specimens with greater corrosion of shear reinforcement.
Finally, the relationship between exterior damage and degree of internal deterioration was examined. As a result, it was confirmed that the relationship with the amount of chloride ion was clear only when the exterior damage was very large. Cracks and corrosion of axial bars were observed, but no relationship was found between PC steel and shear reinforcement bars and cracking, floating, and spalling and steel corrosion. Since not much data was obtained on PC steel in this study, more data should be collected in future surveys.